Frequency and causes of kangaroo-vehicle collisions on an Australian outback highway

Kangaroo-vehicle collisions are frequent on Australian highways. Despite high economic costs, detrimental effects on animal welfare, and potential impacts on population viability, little research has been done to investigate the impact of road mortality on kangaroo populations, where and why accidents occur, and how the collisions can be mitigated. We therefore collected data on species (Macropus rufus, M. giganteus, M. fuliginosus, M. robustus), sex and age of kangaroos killed on a 21.2-km bitumenised section of outback highway over 6 months in far western New South Wales, Australia. The spatial and temporal distribution of road-killed kangaroos was investigated in relation to the cover and quality of road-side vegetation, road characteristics, the density of kangaroos along the road, climatic variables and traffic volume. A total of 125 kangaroos were found killed on the road at a rate of 0.03 deaths km-1 day-1. Grey kangaroos of two species (M. giganteus, M. fuliginosus) were under-represented in the road-kill sample in comparison with their proportion in the source population estimated during the day. No bias towards either sex was found. The age structure of road-killed kangaroos was similar to age structures typical of source kangaroo populations. Road-kills mainly occurred in open plains country. In road sections with curves or stock races, road-kill frequencies were higher than expected. Greater cover and greenness of roadside vegetation at the verge probably attracted kangaroos to the road and variation in this vegetation affected the spatial distribution of road-kills. The temporal distribution of road-kills was positively correlated with the volume of night-time traffic. The probability of a kangaroo-vehicle collision increased exponentially with traffic volume. Results are discussed in relation to the potential for mitigation of kangaroo-vehicle collisions. © CSIRO 2006

Kangaroo-vehicle collisions in Australia's sheep rangelands, during and following drought periods

The effects of roads on wildlife behaviour and ecological function are poorly known in arid Australia. The most obvious impact is roadkill from wildlife-vehicle collisions. Therefore we collected statistics on kangaroo-vehicle collisions, investigated the causal factors of these collisions, and related roadkill mortality to the population structure, size and distribution of four kangaroo species in two intensive six month studies during and following drought. The research was conducted along a 21.2 km sealed section of the Silver City Highway between Broken Hill and Tibooburra that passes through the University of New South Wales (NSW) Arid Zone Research Station at 'Fowlers Gap' in north-western NSW. The rate of roadkill was higher during drought (20.8 roadkills month-1) than non-drought (2.6 roadkills month-1). Affected species were red kangaroos (Macropus rufus), euros (Macropus robustus erubescens), western grey kangaroos (Macropus fuliginosus) and eastern grey kangaroos (Macropus giganteus). During drought, M. fuliginosus and M. giganteus were killed in lower proportions than their proportion in the source population, otherwise species were killed in proportion to their density along the road. There were no sex biases but male M. r. erubescens were much more likely to be beside the road than females and thus were killed more often during drought. The majority of roadkills were young individuals around 2 years old. Curves and stockraces along the road significantly increased the likelihood of roadkills. Likewise the frequency of roadkills was a function of the kangaroo population density along the road, night time traffic volume, low rainfall and higher vegetation cover and greenness along the road relative to surrounding areas. We evaluate the relationships between these causal factors and kangaroovehicle collisions, and discuss the possible effects of these collisions on kangaroo population structure under drought and post-drought conditions